There are a series of known standards that provide a foundation for audio, video, and data communications across a variety of networks. For example, the International Telecommunications Union (ITU) is one standards body that is responsible for the defining these standards. Generally for the ITU, the standards fall in the H.32× series of standards. For example, the H.323 standard is an umbrella recommendation from the ITU that sets standards for multimedia communications over Local Area Networks (LANs). H.320 is another umbrella suite of recommendations, which covers audio/video telephony on switched digital circuits. H.320 establishes standards for compression/decompression of audio and video data streams as well as standards for multiplexing of data streams. Examples of Public Switched Telephone Network (PSTN) protocols that are currently in widespread use that can pass H.320 calls include Signaling System #7 (SS7), Integrated Services Digital Network (ISDN), and other digital protocols to numerous to list that can support at least 56K clear channel calls. By adhering to standards, multimedia products and applications from multiple vendors can interoperate, allowing users to communicate without concern for compatibility.
When a video call is placed between two IP video terminals operating in accordance with the H.323 standard or other IP protocol capable of performing video, supporting video codec H.263, a set of capabilities are typically passed between the two terminals. Normally, all of these capabilities are passed transparently. However, if part of the call between the two terminals contains an H.320 call leg, not all of the H.263 capabilities can be passed transparently. This is due to limitations in the interworking between ITU specifications H.245 on the IP side and H.221/H.242 on the TDM side of the call. For instance, the StandardMPI and Pixel Aspect Ratio Code (PAR) fields within the Custom Picture Format (CPF) part of the capabilities do not exist in the H.242 specification for H.263. Thus, for calls using H.263 that traverse both IP, using H.323 or similar protocol, and PSTN, using the H.320 protocol, parts of the H.263 capabilities are lost. In addition, when a typical call is placed between two IP video terminals, a limited bandwidth connection is opened between the terminals for video. Normally, the maximum allowed bandwidth is used between the two terminals. However, in cases where bandwidth needs to be reduced during a call, a flow control indication may be sent from the terminal requiring the reduction of bandwidth. Unfortunately, when a video call includes an H.320 leg, the IP leg requiring the bandwidth reduction can overflow, causing disruptions in the video stream.